Motors operating upon the principles invented by R. J. L. Moineau many years ago are now quite well known. In all cases, these involve an outer member having internal helical threads and an inner member having external helical threads with the outer member having one more internal helical thread than the external helical threads on the inner member. Thus, if the outer member is held stationary or is caused to rotate on its own axis, the inner member will gyrate within the outer member. If the rotation of the inner member is to be transmitted to a shaft running on true centers, or if the inner member is to be driven by a shaft running on true centers, then it is necessary to provide between the inner member of the motor or pump and the input or output shaft, which is running on true centers, a connecting rod with a universal joint at each end. This construction is shown in many of the earlier R. J. L. Moineau patents.
In earlier patents of Wallace Clark, e.g. U.S. Pat. No. 3,932,072 dated Jan. 13, 1976 and No. 3,951,097 dated Apr. 20, 1976, and No. 4,051,910 dated Oct. 4, 1977, and No. 4,059,165 dated Nov. 22, 1977, various ways of avoiding the double universal joint and connecting rods are disclosed. These patents teach the use of a ball and tube wherein the ball is secured to the end of the internal member of the motor or pump extending at right angles to the axis of the inner member, and is constrained to operate within a tube or between a pair of cheeks. According to these patents, the effective eccentricity is removed from the drive train and the power of a ball arm is used to hold or to drive a concentrically supported hollow shaft as, for example, in a water swivel.
With this arrangement, the ball follows an elliptical path and does not spin as it rotates in the tube or in the half tube or between cheeks, and it cannot cross the axis of the motor.